Why do people try to persuade the suicidal persons?

It seems mysterious to me. Like so many people being killed in places like Iraq, Palestine, Africa because of wars, hunger etc. People don't seem to care for whether people live or die. There are 6 billion people in the world what if millions die nothing would happen. Then if someone wants to commit suicide then why do people try to persuade otherwise. On the other hand all problems are created in the first place by people, don't they? So why to shed crocodile tears?? Why don't we encourage more people to commit suicide??? So that more of us can live a better life????